The structure of chromanes is abundant in natural products that possess a broad array of biological activities such as antimicrobial, antiviral, anti-proliferative and antitumor activity. Since chromanes are found in many natural products, efficient construction of this ring structure has attracted much attention in the recent past.
Synthesis of Chromane Derivatives via Indium-mediated Intramolecular Allenylation and Allylation to Imines as in scheme 1 is disclosed by Han-Young Kang et al. in Bull. Korean Chem. Soc. 2004, Vol. 25, No. 11, 1627-1628. However, the reported yields are poor in the range of 70-80%.

Synthesis of Chromane Derivatives by Palladium-Catalyzed Intramolecular Allylation of Aldehydes with Allylic Acetates or Chlorides using Indium and Indium(III) Chloride as in scheme 2 is reported by Van Cuong Nguyen et al. in Bull. Korean Chem. Soc. 2005, Vol. 26, No. 5, page 711-712. However, the yields reported are poor in the range of 40-80%.

Synthesis of tetralin and chromane derivatives via In-catalyzed intramolecul arhydroarylationas in scheme 3 is reported by Kai Xie et al., in Tetrahedron Letters Volume 51, Issue 33, 18 Aug. 2010, Pages 4466-4469. According to this study, In(OTf)3 was found to be an effective catalyst for the cyclization of ω-aryl-1-alkenes to form tetralin and chromane derivatives.

Though the use of indium provides cost advantage over the use of palladium/platinum catalysts, the cursory review of prior art methods shows that the yields of the chromane obtained are not exceeded 80% and again the purification of the desired product and recycling of unreacted reagents adds additional steps to the synthesis.
Most of the reported methods for synthesis of chromanes are run under harsh conditions with high concentration of Lewis acids, which can hardly be tolerated by many functional groups.
In the light of the above, the present inventors have aimed at the alternate provision of efficient method for the synthesis of important chroman structure that possess a broad array of biological activities such as antimicrobial, antiviral, antiproliferative and antitumor activity.